How do you screw into fiberglass/gelcoat without chipping?

[guy48065]

Yup, this is the way to do it.

He's drilling 9/16 holes for bolts, not for small self-tapping wood screws.
In my case the drilling itself didn't cause any damage so going in reverse wouldn't help. It's the teeth of the screws lifting the gel before they 'bite' and pull in that was the issue.

 

[Texasmark]

When in industry, people who worked certain substances used a peculiar bit. It may be referred to as a "sheet metal" bit. Rather than having a chisel point where the cutting edge starts at the center and as it penetrates the material the bit is slanted and works its way out to the final diameter.

The bits had a small center cutter to maintain position on the material and above that and on out to the OD, the blade was basically flat out to the outer edge where the circumference of the bit was pointed from the mid section to the outer diameter that sloped out to a sharp edge with the OD being inline with the rest of the OD of the bit. The result was that other than the centering point, the OD cut first which kept the circumference from chipping the material and as the bit penetrated, the cut material increased from the OD to the center.

A picture would help....a lot fewer words trying to get the idea across!

 

[Horigan]

He's drilling 9/16 holes for bolts, not for small self-tapping wood screws.
In my case the drilling itself didn't cause any damage so going in reverse wouldn't help. It's the teeth of the screws lifting the gel before they 'bite' and pull in that was the issue.

You need the bevel from a counter sink bit to be deep enough so the OD of the screw threads initially contacts fiberglass and not the gel coat above it.

 

[guy48065]

You need the bevel from a counter sink bit to be deep enough so the OD of the screw threads initially contacts fiberglass and not the gel coat above it.

Agreed.

 

[Jeff J]

Has anyone ever tried the drill bits for putting holes in plexiglass and the like?

 

[froggy1150]

Try the above mentioned bevel/chamfer but before attaching whatever hardware take a screw, add a touch of lube and install just the screw going back and forth to cut threads just like a tap. That way your not cutting and pulling at the same time.

 

[Texasmark]

Has anyone ever tried the drill bits for putting holes in plexiglass and the like?

I have done that and I think this is the type bit I was trying to describe above.

 

[Jeff J]

I had to look it up. General purpose drill bits like most of us have laying around are 118 degrees. The angle will likely be 135 degrees if you drill a lot of steel. The bits for cutting plexiglass are 90 degrees. I haven’t tried it on fiberglass or gelcoat but it makes a huge difference drilling plexiglass, lexan and pvc.

 

[dingbat]

The bits had a small center cutter to maintain position on the material and above that and on out to the OD, the blade was basically flat out to the outer edge where the circumference of the bit was pointed from the mid section to the outer diameter that sloped out to a sharp edge with the OD being inline with the rest of the OD of the bit. The result was that other than the centering point, the OD cut first which kept the circumference from chipping the material and as the bit penetrated, the cut material increased from the OD to the center.

They are called "brad Points"......used to grind our own for drilling sheet metal and "gummy" aluminum

 

[Texasmark]

They are called "brad Points"......used to grind our own for drilling sheet metal and "gummy" aluminum
View attachment 411532

Well that answers the question why I first saw them at work. A lot of sheet aluminum was processed......5052 T6 if I remember correctly after being retired 20 years.

 

[Jeff J]

I have seen brad point drill bits but I had only seen them advertised for cutting wood until today. I just checked the aviation tool suppliers I usually do business with and they have them listed for drilling composites.

I have drilled and watched a lot of holes being drilled in aluminum sheet 0.020”-0.040” thick over the last 40 years and never seen anyone use a brad point. 5052 is pretty hard compared to some of the alloys used in aircraft. I don’t usually have a problem but I had to put a hole in a soft steel firewall that I more poked a hole through than cut with the drill bit. I had to use a dremel to clean it up. I will have to give the brad point a try on thin metal.

 

[cyclops222]

Just remember. Those drills are designed for woods.

 

[dingbat]

5052 is pretty hard compared to some of the alloys used in aircraft.

You have that backwards

The 5XXX series aluminum are “gummy” (soft and bendable) compared to 7075 “aircraft”, or any of the 2XXX series aluminums for that matter, that are much “tougher” (74-78 Ksi).

Grinding a split or brad point allows faster feeds and cleaner/faster chip removal.

that I more poked a hole through than cut with the drill bit. I had to use a dremel to clean it up. I will have to give the brad point a try on thin metal.

Split points solve this problem

 

[dingbat]

Just remember. Those drills are designed for woods.

Not necessarily.
They work equally as well on non-ferrous materials.

 

[Jeff J]

“
You have that backwards

The 5XXX series aluminum are “gummy” (soft and bendable) compared to 7075 “aircraft”, or any of the 2XXX series aluminums for that matter, that are much “tougher” (74-78 Ksi).”

Primary aircraft structure isn’t the only thing that gets holes drilled into it. Try drilling holes in some 3003. On the other hand, nice hole can easily drilled into 2024. Personally, I think fuel and oil lines are the only place I have seen 5052 on an airplane because it does bend easy and is quite a bit stronger than 3003. I am sure I have seen 7075 but couldn’t tell you where or if I have ever drilled into any.

 

[dingbat]

“
You have that backwards

The 5XXX series aluminum are “gummy” (soft and bendable) compared to 7075 “aircraft”, or any of the 2XXX series aluminums for that matter, that are much “tougher” (74-78 Ksi).”

Primary aircraft structure isn’t the only thing that gets holes drilled into it. Try drilling holes in some 3003. On the other hand, nice hole can easily drilled into 2024. Personally, I think fuel and oil lines are the only place I have seen 5052 on an airplane because it does bend easy and is quite a bit stronger than 3003. I am sure I have seen 7075 but couldn’t tell you where or if I have ever drilled into any.

3003 is commercially pure aluminum.
1XXX series is “pure” aluminum, 99% or better. Not much above butter …lol

Did a project with Kaiser Aluminum - Spokane a number of years ago. At that time, they were using 7075 for the skin of the 747. It’s my understand that 7050 is more widely used at this point in time.

Been in steel and aluminum production my entire career. Design and build measurement and QA instrumentation used in production and coating of steel and aluminum. All the major steel and aluminum producers in the world use our equipment in their processes.

 

[Jeff J]

Skin requirements on an airliner are a little different than on a small general aviation airplane. Some new production aircraft are still using Dacron fabric. Many vintage aircraft came from the factory with cotton skin. 2024 aluminum is what I see most for stressed skin. 3003 is more for low stress parts like some cowls and baffles. 5052 tubing makes great fuel, oil and brake lines. The 3003 tubing doesn’t hold a flare well and tends to wear out and break at the fitting.

 

[dingbat]

Skin requirements on an airliner are a little different than on a small general aviation airplane. Some new production aircraft are still using Dacron fabric. Many vintage aircraft came from the factory with cotton skin. 2024 aluminum is what I see most for stressed skin. 3003 is more for low stress parts like some cowls and baffles. 5052 tubing makes great fuel, oil and brake lines. The 3003 tubing doesn’t hold a flare well and tends to wear out and break at the fitting.

Have gotten a chance to work with some interesting developmental metals over the years.
Some of the UHSS steel alloys developed for automotive applications have crazy weight to strength ratios

Interesting note….the original “7075 alloy” was developed by the Japanese for use in the Japanese Zero during WW2. Alcoa backwards engineered the alloy we know today from a captured plane

 

[MikeSchinlaub]

I've never used any specialty drill bits for boats. Just the normal HSS 118° drill bits out of any hardware store. Not the super cheap gold colored stuff though. Those just suck for anything.

My Irwin sets came with split points though. Nice for metal, but gel and glass are so soft that you really don't benefit from it.

Now all that stuff about alloys and fancy drill bits? Way over my head.